PyBOMBS Update issue

Unfortunately, PyBOMBS only support git as remote repo. Your patched recipe repos will make a complex git tree. So we don't want to mess up with a lot of git-cherry-pick git-merge or something.

For now, every time we fetch recipes from upstream, we drop our previously patched commits, generate a new repo. Thus user need to do a refresh git clone, because the mirror recipe git repo we generated doesn't have a continous git tree.